DESCRIPTION: This is a collaborative group investigation to study the potential risks or preventive properties of exogenous hormones and prophylactic surgery for breast and ovarian cancer development in BRCA1 and BRCA2 carriers. The goals of this study are to: 1) identify families with BRCA1 and BRCA2 mutations; 2) establish whether oral contraceptive use protects against ovarian cancers in carriers of BRCA1 mutations; 3) establish whether tubal ligation protects against ovarian cancer in carriers of BRCA1 and BRCA2 mutations; 4) establish whether oral contraceptive use increases the risk of breast cancer in BRCA1 and BRCA2 mutation carriers; 5) establish whether hormone replacement therapy increases the risk of breast cancer in carriers of BRCA1 and BRCA2 mutations; 6) establish if oophorectomy is associated with a reduction in mortality from ovarian cancer in comparison to observational therapy; 7) establish if an oophorectomy reduces the risk of breast cancer; and 8) establish if a prophylactic mastectomy reduces the mortality from breast cancer in comparison to mammographic screening.